Oil-sealed vane rotary vacuum pump

ABSTRACT

An oil-sealed vane rotary vacuum pump includes at least one pump stage arranged in the housing and having a cylindrical chamber, a shaft excentrically arranged in the cylindrical chamber and provided with vanes, and a drive for driving the shaft and having a plurality of permanent magnets arranged on the shaft and stationary electrical coils surrounding the permanent magnets and producing a rotatable magnetic field, and control electronics for controlling the coils and arranged in a removable housing part of the pump.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oil-sealed vane rotary vacuum pump including a housing, at least one pump stage arranged in the housing and having a cylindrical chamber, a shaft excentrically arranged in the cylindrical chamber and provided with vanes, and drive means for driving the shaft.

2. Description of the Prior Art

Vane rotary vacuum pumps play an important role in generation of vacuum. They are used to generate low and high vacuum with an end pressure up to about 6*10⁻³ mbar and are used in industry, research, and laboratories. Traditionally, these pumps are used as for vacuum pumps for pumps such as Roots vacuum pumps and turbomolecular pumps which are not sealed against the atmospheric pressure. Dependent on their use, they are formed as one stage or multi-stage pumps.

The vane rotary vacuum pumps of the type described above belong to a class of oil-filled positive displacement pumps. The oil performs in such a pump several functions, among them are sealing the gas outlet side from the gas inlet side, cooling functions, lubrication of mechanical components of the pump.

However, oil adversely affect the design of the drive motor. At the start of the operation, when the pump is cold, the oil is thickflowing and glutinous. Therefore, very much power is required at the drive motor side for rotating the pump rotor. With inadequate dimensions of the motor, i.e., with a low torque of the drive motor, the pump may not even start. As a remedy, a high-viscous oil can be used. However, such oil includes volatile components which increases the end pressure (see Wutz, Handbuch Vakuumtechnik (Vacuum Technology Handbook) Vieweg-Verlag, 8te Auflage (8^(th) edition), S. 202 ff). As it is not possible to use a high-viscous oil in many applications, the drive motors of oil-lubricated vane rotary vacuum pumps are made very powerful.

The vane rotary vacuum pumps of the type described above conventionally are equipped with asynchronous alternating current electric motors. The relationship between their torque and the rotational speed is shown in FIG. 3. At low rotational speeds, the torque is low. A noticeably higher maximal torque is reached at intermediate rotational speeds. At high rotational speeds, the torque falls again. These facts leads to overdimensioning of the drive motors in order to be able to start the vane rotary vacuum pump. The overdimensioning results in an unnecessary power consumption of the drive motor which increases both the manufacturing costs and the operational costs. The later play a particularly important role as a vane rotary vacuum pump is designed for a continuous duty.

The over dimensioning of the drive motor also negatively influences the size of the entire pump. A compact volume, which is required by contemporary pump stands and plants, cannot be achieved on the basis of the stand-of-the art drive motors. This is further aggravated by the fact that the electrical energy, which is not converted into the rotation of the rotor, is converted into heat which has to be removed. The heat within the pump stand should be removed, if needed, by active cooling.

Alternating current motors, which are used in particular in small and intermediate vane rotary vacuum pumps with a suction capacity up to 40 m³/hr, are often formed as two-phase motors. These motors are provided with capacitors in order to be able to use more than two coils per circumference. This results in a non-uniform torque characteristic, i.e., in non-uniform torque per a shaft revolution. As a result, unnecessary high vibration and noise are produced, which in many applications are hardly tolerated. Therefore, suitable installation measures need be undertaken to prevent transmission of these vibration to sensitive laboratory apparatuses.

The oil in the vane rotary vacuum pump serves, as it has already been discussed above, for cooling, lubrication of movable parts, and for sealing the compression chamber. With the use of oil, the contamination of the pump surrounding with oil that exits the housing takes place. This contamination should be prevented. Sealing of the location where the rotor extends through the housing is difficult. Traditionally, for sealing these locations, radial shaft seals are used which are characterized by high wear. This increases maintenance costs. In order to eliminate the drawbacks of these seals, the conventional pumps are equipped with magnetic couplings and split pot elements, which leads to increased manufacturing costs and reduced operational costs. State-of-the-art vane rotary vacuum pumps have a drive system with two shafts, rotor shaft and motor shaft. Both need be adequately supported. In addition, coupling elements between the shafts should be provided. This increases the number of components, assembly costs, and increase chances of failure.

Accordingly, an object of the present invention is an oil-sealed vane rotary vacuum pump in which the drawbacks of the state-of-the-art oil-sealed vane rotary vacuum pumps are eliminated.

SUMMARY OF THE INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing, in an oil-sealed vane rotary vacuum pump, drive means for driving the shaft and having a plurality of permanent magnets arranged on the shaft and stationary electrical coil means surrounding the permanent magnets and producing a rotatable magnetic field, and control electronics for controlling the coil means and arranged in a removable housing part of the pump.

According to the invention, the oil-sealed vane rotary vacuum pump is equipped with brushless direct current motor that consists of permanent magnets arranged on the shaft of the pumping system, and stationary coils which are controlled by the control electronics. These motors have a very uniform relationship between the torque and rotational speed and rotational angle. Thus, already at a very low rotational speed, the motor starting torque is brought up to almost a full torque. Thereby, a motor can be used that has, in comparison with an asynchronous alternating current motor, a uniform torque and a noticeably reduced power consumption. In addition, the motor has reduced dimensions and, therefore, the pump itself can be formed more compact. Further, the uniform torque provides for a noticeably quieter running, which positively influences the vibration and noise. Further, instead of several shafts used in conventional pumps, only one shaft is used, which reduces the manufacturing costs and the danger of failure.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing shows:

FIG. 1 a vane rotary vacuum pump according to the present invention with permanent magnets arranged on the pump shaft and coils that produces a rotatable magnetic field;

FIG. 2 a vane rotary vacuum pump according to the present invention with permanent magnets arranged on the pump shaft and coils that produces a rotatable magnetic field, and a split pot member; and;

FIG. 3 a diagram showing relationship between a rotational speed and a torque for an asynchronous alternating current motor (continuous line) and for direct current motor (dash line).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An oil-sealed, vane rotary vacuum pump 1 according to the present invention, which is shown in FIG. 1, includes a housing 2 having a gas inlet 3 and a gas outlet 4, and a pumping system 5 located in the interior of the housing 2. The pumping system 5 includes a shaft 12 which is supported in bearings 13. The pumping effect is produced by rotation of the shaft 12 together with rotary vanes 7. A hydraulic oil pump 6 provides for lubrication of the bearings 13 which are formed as bearings and supplies a high vacuum safety valve 20 with oil. This safety valve 20 is closed when the shaft 12 does not rotate any more, which leads to reduction in oil pressure provided by the oil pump 6.

On the shaft 12, there are arranged a plurality of permanent magnets 14 which are surrounded by coils 10. The coils 10 produce a rotatable magnetic field the position of which changes by an electronic commutation and thereby provides for rotation of the shaft 12. Instead of two shafts of conventional pumps, namely, rotor shaft and motor shaft, the inventive pump 1 has only one shaft, shaft 12. Sensors 16, preferably Hall sensors, are used for determining an angular position of the shaft 12. The sensor signals from the sensors 16 are communicated to control electronics 8. The control electronics 8 is preferably arranged in a removable part of the housing 2 which is, in particular, sealed from the oil space. The control electronics is supplied with energy through a cable that can be connected to an available supply network, such as, e.g., an alternating current network with a voltage of 230V or an industrial voltage network (e.g., of 24V or 48V).

According to an advantageous embodiment of the present invention, the control electronics 8 can operate with one- or multi-phase network voltage between 60V and 400V. A selector switch permits to select a respective voltage. It is advantageous when the control electronics 8 is provided with means that automatically recognizes the applied voltage. The foregoing means insure that the inventive vane rotary vacuum pump can operate with all voltages used throughout the world. As a result, high mounting costs can be spared as the pump needs not be adapted to specific local conditions. Instead, standard components can be used for pump that can operate worldwide.

The control electronics 8 contains a power element 9 for driving the coils 10. It is advantageous when the power element 9 forms a thermal contact with the wall of the housing 2. In this case, the heat from the pump 1 is removed by thermal convection, which permits to eliminate an additional cooling means.

Advantageously, the coils are encapsulated in a cast plastic material or resin so that oil and oil residue should not corrode them, which could lead to their distortion. The oil residues occur in fields of the pump applications in which corrosive or other process gases are pumped.

According to an advantageous embodiment of the present invention, the control electronics 8 provides for rotation of the shaft 12 with different, selectable by a pump user, rotational speeds and, thereby, provides for regulation of the suction capacity of the pump. The hydraulic pump should be so formed that in order to supply the bearings with oil and to open the high vacuum safety value 20, it provides for built-up of sufficient oil pressure even in the low region of rotational speeds. Then, the pressure relief valve in the oil circuit should open at high rotational speeds in order to prevent high pressure.

According to a further advantageous embodiment of the present invention, the oil pump is dispensed with. Instead, an electromagnetic high vacuum safety valve is used which is controlled by the control electronics 8 via a cable 22. When the control electronics 8 ascertains that the shaft 12 does not rotate anymore, it switches the electromagnetic high vacuum safety valve to the valve closed condition.

According to a still further advantageous embodiment of the present invention, the housing part, which houses the control electronics 8, is located within the pump housing.

The embodiment of the inventive pump, which is shown in FIG. 2, differs from that of FIG. 1 in that the vane rotary vacuum pump, which is shown in FIG. 2, includes a split pot member 18 which is arranged between the shaft 12 and the coils 10. The split pot member 18 permits to arrange the coils 10 outside of the oil-filled space. The split pot member 18 is formed of a non-magnetic material, e.g., ceramics.

Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

1. An oil-sealed vane rotary vacuum pump, comprising: a housing; at least one pump stage arranged in the housing and including a cylindrical chamber, a shaft excentrically arranged in the cylindrical chamber and provided with vanes, and drive means for driving the shaft and having a plurality of permanent magnets arranged on the shaft and stationary electrical coil means surrounding the permanent magnets and producing a rotatable magnetic field; and control electronics for controlling the coil means and arranged in a removable housing part of the pump.
 2. An oil-sealed vane rotary vacuum pump according to claim 1, further comprising a split pot member arranged between the shaft and the coil means for separating the pumping chamber from atmosphere.
 3. An oil-sealed vane rotary vacuum pump according to claim 1, further comprising sensor means for determine a position of the pump shaft.
 4. An oil-sealed vane rotary vacuum pump according to claim 3, wherein the sensor means comprises Hall sensor means.
 5. An oil-sealed vane rotary vacuum pump according to claim 1, wherein the control electronics includes means for changing the rotational speed of the shaft.
 6. An oil-sealed vane rotary vacuum pump according to claim 1, wherein the control electronics is directly connectable with a supply network.
 7. An oil-sealed vane rotary vacuum pump according to claim 6, wherein the control electronics is connectable with one- or multi-phase voltage between 60V and 400V.
 8. An oil-sealed vane rotary vacuum pump according to claim 1, wherein the control electronics comprises power means for operating the coil means and wherein at least the power means forms a thermal contract with a wall of the pump housing.
 9. An oil-sealed vane rotary vacuum pump according to claim 1, wherein the coil means is encapsulated in one of cast plastic material and resin.
 10. An oil-sealed vane rotary vacuum pump according to claim 1, wherein the removable housing part, which contains the control electronics, is located in the pump housing. 